1. Technical Field
The present disclosure relates to a material for contact lenses, and more particularly, to a method for manufacturing a hydrophilic silicone prepolymer for making contact lenses.
2. Description of Related Art
Traditional contact lenses may result in corneal hypoxia due to the lack of oxygen and are not suitable for a prolonged wearing. At present, silicone hydrogel lenses in the market all declare having high oxygen permeability. Since the contact lens made of silicone hydrogel allows sufficient oxygen directly through the lenses to the cornea, silicone hydrogel has become one of the preferable classes of contact lenses.
However, since silicone hydrogel is mainly composed of silicone, which is hydrophobic in nature, silicone hydrogel is still causing corneal relatively dehydrated, dry and irritated. In this regard, how to keep the silicone hydrogel lens moisturizing is the most challenging issue in the industry. There are some methods which keep silicone hydrogel lens moisture comprising: performing a surface treatment of the silicone-rich hydrophobic lenses by a plasma process, adding polyvinylpyrrolidone into the silicone hydrogel formulation and using a silicone prepolymer having a polyoxyethylene side chain.
Silicone hydrogel lenses are typically made from one or two kinds of silicone monomer, polymer or prepolymer, and these silicone components are hydrophobic. Silicone monomers typically have molecular weights less than 500 and with up to 4 silicon atoms in their structure, for example, 3-(methacryloyloxypropyl)-tris(trimethylsiloxy)silane (TRIS). Silicone macromers usually have a number average molecular weight of about 500 to 1,100, and these macromers have linear multiple siloxane units and single ethylenically unsaturated group. Silicone prepolymers have at least two ethylenically unsaturated groups and have repeating units of linear multiple siloxanes. Although Keogh et al. in 1981 disclosed some structures of these silicone macromer or prepolymer (U.S. Pat. No. 4,259,467), only the hydrophilic silicone prepolymer having a polyoxyethylene side chain was synthesized and used in the manufacture of silicone hydrogel lenses. (U.S. Patent Application Publication 2006/0063852). No manufacturing methods for other hydrophilic group-containing hydrophilic silicone prepolymers have ever been proposed.